How Dose Inverter Work ?
Author: Source: Datetime: 2016-09-14 17:49:39
As a solar photovoltaic system applications inverters have special requirements on the design and use a lot. Such as
① instantaneous peak output power and power requirements;
② inverter output efficiency requirements;
③ inverter output waveform requirements;
④ inverter input DC voltage.
These four indicators have become a test of the inverter technical performance of important content.
We already know that the array of PV modules, charge controller and lifePo4 batteries system constituted only produce direct current, alternating current if the load needs, there must be an inverter which is capable of DC to AC inverter (see Figure 5-5) . If necessary, the inverter is divided into two types of single-phase and three-phase, frequency of common 50/ 60HZ, voltage 110V or 220V, and can provide continuous power output from a few hundred to several kilowatts. Large inverter can output 380V, voltage Gao even more, and more than 10kW, 100kW or more power.
The basic principle of the inverter
Inverse transformation and transformation on the contrary, it uses full-controlled power devices having switching characteristics, controlled by a certain logic, switch control signal issued by the main control circuit of the power device periodically, and then transformer coupled liter (or decreasing) the pressure shaping filter get AC we need. Usually small and medium-power inverter with power FET (MOSFET), insulated gate transistor (IGBT), high power inverters adopt turn-off thyristor (GTO) devices.
This is a simple use of an inverter circuit composed of MOSFET power switch. Its essence is a push-pull inverter circuit, the step-up transformer neutral tap connected to the positive power supply, two power transistors SW1, SW2 alternately, solar power portable generation the output obtained AC power. Since the power transistor connected to common ground, and the drive control circuit is simple, while the transformer has a certain leakage inductance to limit the short circuit current, thereby improving the reliability of the circuit. The disadvantage is low efficiency transformers poor ability with inductive loads.
This is a full-bridge inverter circuit formed by the power switch. Full-bridge inverter circuit to overcome the shortcomings of push-pull circuit in Figure 5-6, the power switch SW1, SW2 and SW3, SW4 inverted, SW1 and SW3 phase difference 180 °, adjust SW1 and SW3 output pulse width, output AC RMS voltage, that changed. Control signal four power switches is given by the main control circuit, since the circuit has to make SW2 and SW4 common conduction function, which has a freewheeling, even for inductive load, the output voltage waveform is not distorted. The disadvantage of this circuit is on the lower arm power switch is not common ground, portable power generator is necessary to use special driver circuit, or with isolated power. In addition, to prevent the upper and lower arm turned common occurrence in SW1, SW2 and SW3, SW4 must be designed to shut off between the conduction circuit, which must be set dead time, is given by the main control circuit.
Topology PV inverter main circuit is the use of more tertiary structure (DC AC DC-AC), there is also a single-stage (DC-AC) or two (DC-DC-AC) structure. In general, small and medium power PV systems PV array DC voltage which is not too high, and high current power switches rated withstand voltage values are relatively low, and therefore relatively low voltage inverter to get 220V or 380V AC, either push-pull or full bridge inverter circuit, which must be added to the output of the step-up transformer, generally use two topological structure, tertiary structure. Since the frequency step-up transformer bulky, inefficient, expensive prices in recent years, with the development of power electronics and microelectronics technology, the use of Gao frequency switching and soft switching inverter technology, the power generator density can be achieved Gao inverter, the first stage booster circuit this inverter circuit using a push-pull structure, but were operating frequency above 20kHz, using high-frequency step-up transformer core material, so small size, light weight, after Gao frequency inverter through High-frequency transformer into high frequency alternating current, and after Gao Gao frequency rectifier filter circuit to obtain a DC voltage (generally in 300V or more), and then by frequency inverter circuits get 220V or 380V AC inverter, inverter efficiency in the system 90 % or more, currently available commercial sine wave inverter is more is that this tertiary structure, solar power portable generator working principle is: first PV square output low voltage (such as 24V, 48V, 110V also above) by the high DC frequency (several kHz to several tens kHz) square wave AC inverter AC, through the step-up transformer rectifier filter becomes a high pressure (110V or more) DC DC, and then by the third stage DC-AC inverter is required frequency alternating current (220V or 380V).
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